In recent years, a ring-opened polymer of a norbornene monomer having a functional group as a substituent (hereinafter may be referred to as “functional group-containing norbornene monomer”) and a hydrogenated product thereof have attracted attention as functional group-containing polymers exhibiting excellent heat resistance, electric characteristics, low water absorption, and the like. These polymers also exhibit excellent adhesion to an inorganic material such as a metal or glass and excellent compatibility with an organic material such as an antioxidant, plasticizer, UV absorber, coloring agent, curing agent, or flame retardant, and, therefore, are expected to be used for various composite materials.
Conventionally, as a process for producing such a functional group-containing polymer, a process of obtaining the polymer by ring-opening polymerization, using a metathesis polymerization catalyst, of a norbornene monomer having a functional group at either the 5-position or 6-position, or both positions as substituents, obtained by Diels-Alder addition reaction of cyclopentadiene with a functional group-containing olefin such as acrylate, methacrylate, acrylonitrile, maleic anhydride, or maleimide have been known, for example (Japanese Patent Application Laid-open No. S50-58200; Japanese Patent Publication No. S60-43365; Polymer, Vol. 39, Number 39, No. 5, pp. 1007–1014, 1998; Macromolecules, Vol. 33, p. 6239, 2000; etc.).
As another process for efficiently producing a functional group-containing polymer, a process of ring-opening polymerization, in the presence of a metathesis polymerization catalyst, of tetracyclododecene having a functional group at either the 8-position or 9-position, or both positions, as substituents, obtained by Diels-Alder addition reaction of a norbornene monomer having a functional group at either the 5-position or 6-position, or both positions, as substituents, with cyclopentadiene (Japanese Patent Application Laid-open No. H1-132626, WO 01/42332, etc.).
However, these processes require a large amount of a polymerization catalyst in order to obtain a ring-opened polymer at a high yield, because the functional group-containing norbornene monomer used as a raw material has low polymerization reactivity. Further, the functional group-containing norbornene monomer has low polymerization reactivity as compared with a norbornene monomer having no functional group. When copolymerizing these monomers, a large amount of the functional group-containing norbornene monomer is required, and a copolymer having a desired composition ratio and molecular weight is not obtained in some cases. In addition, a norbornene monomer having a carboxyl group as a substituent has particularly low polymerization reactivity. Even if the monomer is polymerized by ring-opening polymerization as is, a ring-opened polymer can not be efficiently obtained.
Therefore, a norbornene ring-opened polymer having a carboxyl group as a substituent has been conventionally produced by a process of polymerizing a norbornene monomer containing an ester group by ring-opening polymerization, optionally hydrogenating the polymer, and hydrolyzing the ester group introduced into the polymer (Japanese Patent Application Laid-open No. H5-97978, Japanese Patent Application Laid-open No. 2001-139776); a process of polymerizing a norbornene monomer containing a carboxylic anhydride group by ring-opening polymerization, optionally hydrogenating the polymer, and hydrolyzing or alcoholizing the carboxylic anhydride group introduced into the polymer (Japanese Patent Application Laid-open No. H11-130843); or the like. However, these processes require an additional step of hydrolyzing (or alcoholizing) an ester group or acid anhydride group after the polymerization step, and are operated in a complicated manner.
In the Diels-Alder addition reaction of cyclopentadiene with a functional group-containing olefin, a norbornene monomer having a functional group at either the 5-position or 6-position, or both positions, is obtained as a mixture of an endo isomer and an exo isomer, in which the production of the endo isomer is generally larger than that of the exo isomer. It is known that, when a functional group-containing norbornene monomer is polymerized by ring-opening polymerization in the presence of a metathesis polymerization catalyst, the exo isomer in the functional group-containing norbornene monomer is easily polymerized, whereas the endo isomer is polymerized in a low polymerization rate and a low polymerization conversion rate (e.g. Macromolecules, Vol. 33, pp. 6239–6248, 2000; Polymer, Vol. 39, pp. 1007–1014, 1998).
Therefore, in the production of a ring-opened polymer of a functional group-containing norbornene monomer, many attempts of separating and purifying only the exo isomer in the functional group-containing norbornene monomer or isomerizing the endo isomer in the monomer to the exo isomer have been made.
However, in order to obtain a high-purity exo isomer, the process must involve a separation and purification step or an isomerization step, which requires much labor.
The present invention has been achieved in view of these problems of the prior art. An object of the present invention is to provide a norbornene ring-opened polymer obtained by ring-opening polymerization of a functional group-containing norbornene monomer that is easily available and has a high polymerization reactivity, a hydrogenated product of the polymer, and processes for producing these polymers.